Guo Yu: A High Efficiency, Broadband Free-space Optical Delay Line for Quantum Memory
A High Efficiency, Broadband Free-space Optical Delay Line for Quantum Memory
Biography: Yu Guo is a PhD candidate at the Centre for Quantum Technologies, National University of Singapore, under the supervision of Prof. Alexander Ling in the SpooQy Lab. His research interests include quantum optics, quantum communication, and quantum networks. His current research focuses on developing a delay-line based optical quantum memory based on a nested Herriott cell. He designed and constructed the device and characterized its performance in both classical and quantum regimes, including its ability to preserve polarization states and energy-time entanglement. His work has resulted in several publications, including an article in APL Photonics that was featured on the cover of the issue. He received his M.Sc. in Computer Science from Nanjing University, where he worked on post-processing algorithms for quantum key distribution (QKD).
Abstract: Quantum networks rely on the distribution and processing of photonic quantum states across remote nodes. An important requirement in such networks is the ability to temporarily store and synchronize photons. This is particularly important in quantum repeater protocols, where independently generated photons need to arrive at a node at the same time for a Bell-state measurement. Quantum memories therefore must not only store photons efficiently, but also to preserve the quantum information encoded in them. In this talk, I will present a free-space optical delay line based on a nested Herriott-cell architecture, and show how it can delay photons while preserving the quantum information they carry. The delay time is tunable in discrete steps, ranging from a few nanoseconds to several hundred nanoseconds. Free-space propagation together with highly reflective mirrors keeps the transmission high even at long delay times. The system also offers an exceptionally broad acceptance bandwidth, providing flexibility for wavelength- and frequency- multiplexed operation. Preservation of polarization-encoded quantum states through the delay line has also been verified by quantum process tomography. Beyond states encoded in a single degree of freedom, I will discuss the preservation of polarization–energy-time hyperentanglement, including measurements of polarization entanglement and energy-time interference after the delay line. Finally, I will present our ongoing work on integrating optical switching for multiplexing and on-demand control, and discuss the potential role of such free-space delay-line quantum memories in future photonic quantum networks.
